1. Field of the Invention
The present invention relates to a hub reduction gear drive unit including epicyclic gearing for mounting in a hub of a vehicle, for example, a road vehicle, tractor, off-highway vehicle or the like vehicle.
2. Description of Prior Art
Where it is necessary to drive a hub whether steerable or not at a reduced speed relative to that of its drive shaft it is well known to provide an epicyclic gear train in the hub. In such cases, the drive is delivered from the vehicle transmission through a drive shaft, commonly referred to as a half shaft, which is rotatable in a stationary hollow axle. A sun gear on the drive shaft meshing with planet gears drives the hub through a planet gear carrier fast on the hub. The planet gears mesh with a stationary annulus gear fast on the axle. Because of this construction, in general, it is essential that the hub be rotatably supported on the stationary axle on bearings which are mounted on the periphery of the axle. Accordingly, this imposes a restriction on the cross-sectional area of the axle where the bearings are supported. Therefore, in order that the axle be of adequate strength it is either formed from a steel forging or pressings welded together.
This does not present problems in the case of large volume production. However, because of the high cost of tooling for either forging or pressing, it is not economically feasible to make such an axle for small volume production, and in general, in such cases epicyclic gear trains cannot be used.